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Ulric

Channelling my Inner Frenchman: The clandestine bicycle SMG

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So, in the time between the suppressor design that I am doing for work, I decided to go after a semi clandestine manufactured SMG. The criteria driving the design is that round tube is incredibly common in SMG designs, so I wanted to avoid that and use rectangular tube and bar stock. This minimizes the operations that require a lathe, and while they ideally would be done on a mill, they can be accomplished with a drill press and hand tools if you have the patience. Some of these parts are innocuous enough that they could also be farmed out to local machine shops without raising eyebrows. Strangely, one of the larger issues that has faced clandestine small arms manufacturing is an acceptable human interface. Other people solve this by traditional methods such as carved wood grips, or cast/molded plastics, but that is a time consuming process to make a part that should be very simple. My solution was to use handlebar grips from a bicycle. They are already designed to provide a griping surface for your hands, and they are common enough and varied enough that you could will not have a problem sourcing them.

 

As far as the design goes, it is still a work in progress. The receiver is pretty much dialed in, as are the trunnions, the barrel, barrel retention system, etc. The FCG has been a sticking points, as designing them is probably my greatest weak point when it comes to arms design. As the FCG is horribly incomplete, the bolt may similarly undergo changes. It is currently planned to have a linear hammer, but that is still in the works. I have only begun to consider what to do for the stock, and the forearm will probably come last. The design uses Uzi magazines, and I'm toying with the idea of being able to change magazine compatibility by having alternate lower receivers.

 

There are two primary versions; the 9" barrel original design, and the 5" barrel design.

 

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Early assembly

 

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Charging handle/bolt/action spring interface

 

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Early receiver, designed to be cut out of 1x2" 11ga rec steel tube. The notches near the trunnion and front barrel support are to allow the components to be welded together.

 

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charging handle and barrel retention system details. The action spring guide rod runs through the front barrel support and in conjunction with the receiver it locks the barrel retainer plate in place. The retention plate slips into a grove cut into the barrel. This prevents the barrel from moving backwards out of the receiver, while the square section at the breech of the barrel nests in the trunnion to prevent forward movement. The barrel is not rigidly fixed to the receiver, but this is acceptable considering the intended applications of the weapon.

 

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I cooked up some bolt variations to utilize different materials for manufacturing. All of these bolts are for the 9" barreled version.

 

The top bolt uses 3/4" 11ga tube, and requires a different bolt face than the other models. It comes in rather light at 420 grams

 

The middle bolt is the update of the original. It is machined out of 3/4x1" bar stock. Weight is 500 grams.

 

The bottom bolt is made out of 1" DOM tube with .250" wall thickness. This involves more external machining than the original, but the channel for the action spring doesn't have to be cut. This is the heaviest at 560 grams.

 

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updated and simplified lower receiver. This is a fixed stock right now, but I want to make a folding version. Current weight is 2.71kg, and it will still increase slightly when I add the FCG, magazine catch, and sights.

 

I updated the bolt for the 5" barreled version, and it now weights 420 grams, the same as the light bolt for the 9" version.

 

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updated receiver architecture to accommodate the new lower.

 

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Thanks to @Collimatrix for jump starting my designers block with the linear hammer idea. previously I was doing stupid things with it, but this is actually worked out really well and even manages to incorporate a concept that I had for the linear hammer from the very beginning. There are still details that need to be worked out, but this is a much idea to work with than what I had before. Side benefit of this, I have increased the bolt mass to 470 grams, so it's closer to where I am comfortable with. That is still relatively light for a 9mm blow back, but it should work.

 

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Overall wire frame of the current design.

 

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My incredibly French front sight post. I plan on shamelessly copying HK sights, but in a simplified form. It will still consist of a rather generous circular front sight hood with the post in the center of it, and all of the adjustment will be done to the rear sight.

 

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